1. Field of the Invention
The present invention relates to techniques for performing an active profiling of the sound emitted by a vehicle engine that issues first acoustic waves along a primary path of propagation of acoustic waves, in particular an exhaust duct. More specifically, the present invention is directed toward such a method including
injecting, via an acoustic-wave diffuser, into a secondary propagation path that merges in said primary path, second acoustic waves that are able to combine with said first acoustic waves in a merge point in said primary propagation path and to generate third resulting acoustic waves; and
generating a signal for driving the aforesaid diffuser by regulating the amplitude of harmonics of the driving signal as a function of reference acoustic waves and of a workpoint of the engine.
The above techniques are described herein with specific reference to internal-combustion engines; however, they may refer to other types of engines, for example electric engines.
2. Description of the Related Art
It is known in the automotive sector to use systems for so-called active sound profiling, which aim at reproducing a given sound profile. Active-sound-profiling techniques can be adopted, for example, for improving the quality of sound inside the passenger compartment of motor vehicles for transport of passengers by modifying the noise of the engine within the passenger compartment. This modification may envisage that the noise of the engine is modified so as to be similar to that of the engine of another model of motor vehicle, for example a prestige-level automobile.
An active-sound-profiling system normally envisages use of an electronic control unit, which, on the basis of internal information that it receives at input regarding the workpoint of the internal-combustion engine, actuates a diffuser in the exhaust system, in particular downstream of the gas after-treatment system. This system has the purpose of injecting, in addition to the sound actually emitted by the engine itself, a precise set of acoustic waves (harmonics) with frequencies corresponding to the current engine workpoint (pedal/r.p.m. and load/fuel). The amplitudes of the injected waves are tuned to follow the amplitudes associated to another motor vehicle that is defined as “target vehicle” at each engine workpoint. In this way, the original sound of the motor vehicle is coloured and becomes similar to the sound of the target vehicle. The waves to inject, i.e., the frequencies to inject, and their amplitudes are selected on the basis of the waves that identify the target sound (i.e., in the target-sound spectrum) of the target vehicle so as to imitate its tone.
FIG. 1 illustrates a principle diagram of an active-sound-profiling system, designated by the reference number 10. In general, an engine 11 comprises a primary exhaust path 13, along which the sound of the engine 11, i.e., the acoustic waves EW, propagates. Inserted along the primary path 13 is a system 12 for after-treatment of exhaust gases. Appearing at the outlet of the primary path 13 is a microphone 18 for measuring the sound. The active-sound-profiling system 10 moreover comprises a secondary exhaust path 17, giving out into which is a diffuser or speaker 16, the secondary path converging in the primary path 13 in a merge point downstream of the exhaust-gas after-treatment system 12 and upstream of the outlet of the primary path 13 and of the microphone 18. The active-sound-profiling system 10 moreover comprises an ESPU (Electronic Sound-Profiling Unit) 15. The ESPU 15 receives from an ECU (Engine Control Unit) 14 information regarding a workpoint WP of an engine 11, in particular, for example, an internal-combustion engine. This information regarding a workpoint WP includes, for example, a number of values of engine r.p.m. ER and/or the signal indicating the gas-pedal percentage GP, i.e., the position of the accelerator pedal expressed as a percentage. The electronic sound-profiling unit 15 drives a speaker 16 via a driving signal SP in order to generate second acoustic waves MW injected into the secondary exhaust path 17, which add to the engine acoustic waves EW in the primary path 13, downstream of the after-treatment system 12, in the merge point with the secondary path 17, so that at output from the primary path 13 third resulting acoustic waves RW are formed, which identify an engine sound different from the sound identified by the first waves EW, which correspond to the original sound of the engine 11 and can be measured, for example, using the microphone 18. Clearly, the microphone 18 does not form part of the system in normal running conditions of the vehicle, and has the calibration purposes what will be illustrated in what follows.
A problem of known systems is to tune with sufficient accuracy the amplitudes of the injected acoustic waves to obtain the desired resulting acoustic waves.